Grigori Perelman, who became famous because of turning down the Fields Medal, including a million dollar prize, for proving the Poincare conjecture, 100 year old standing problem, despite living in near-poverty. Stuff of legends.

He also figure in sibling comment list. I read a book called Perfect Rigor, in that if I remember right, he could easily solve all the seven problems. Which happens rarely. Surely a living (and also tragic) genius. I get goose bumps just by typing this comment.